Differential pressure switch



Oct. 20, 1953 E. E. HARRIS DIFFERENTIAL PRESSURE SWITCH 2 Sheets-Sheet l Filed June 50, 1950 E. E. HARRIS DIFFERENTIAL PRESSURE SWITCH oct. 2o, 1953 2 Sheets-Sheet 2 Filed June 30 1950 EL/ E. HAIER/5) Wd) /QVTTO Patented Oct. 20, 1953 DIFFERENTIAL PRESSURE vSWITCH 7 Eli;v E.. Harris,l Clayton, Mo., assignor :tor-Essex... Manufacturingo., Inc., St. Louis,.M0.,. acorporationolMis'souri ApplicationJune'SO, 1950, Serial Nol171,47'5

12 Claims..v (Cl. 200-81.5).

The :present inventionmelates generally; to .theA

switch art. and morev particularly to a novelfdifferential pressure switch employing afdouble Adiaphragm :and which: is. especially advantageous..v

for use on vaircraft and in.other:installations` where a switch is subjected to extreme ftemperaJ tureA changesgimpact' and vibration, and rwhere extreme Ysensitivity is desired.

In.y its preferred form,`v the switch.' comprises a housing havingva pairof spaceddiaphragms dis-` divideit into an innery .chamber and a `pair .of outer chambers, thev outer 'chambers'beingfin, communication. Ther diaphragms are preferably of the same shape and vsize and have' substantially.. the samemass, thesamecoefcient of expansion;

and the same vibrationcharacteristics. There one. passageway into. thev innerxchamberxand anotheivpassageway into the; outer chambers; A

contactisfastenedy to eachdiaphragmadjacent its' center on. the inner chambenside.:V An ada justable supporting member, which can be justed from outsidethe-honsingf, extends into the innery chamber, and a wedge-shaped member oi.

posed withinthe interior of the housing so as-'to n;

electricity conductingf'materialis. fastened to the` i5 inner end of the supporting member, but electrix-p cally insulated therefromiso as to be movable between the contacts onxthediaphragms; the diaphragme are made of electricity .conduct-- ingv material which isithepreferredconstruction;`

a wire is fastened to eachidiaphragmadjacent its edge; Whereas, `if .the .vdiaphragmsare `made. of.. non-conducting material; the wiresrare connected fdirectly to, the4 contacts. Thus, when'the.` pressure i in the-nuten chambers exceeds that inthe innerg:

chamberby ya lpredetermined amount? the :diae: phragms; and the; contacts 'thereon'.are'forced. ini

wardlyagainst .the..wedge:-.shaped. member, sopas.;

When 5 to complete the electrical..circuitffbetween the,

wires.

As .is-,Lwellknown to those familiar. withr the art; switches; .which are A:usedL on aircraft and. .the like.l

are4v subjected 1to1. rrelatively sudden *temperature* changes of as much;aszseveral.hundred degrees;h

F., impact andvibration: In addition,y in switches of this typegvhighsensitivity'isrequired.

It is:an,objectoi thezpresent invention; .there-eA foie to. p-fprovide:v navel i,differential` pressure; switch.' which.k is not` adversely affe'ctedffby 'tema perature change, sudden impact or vibration,` andi z whichfis very sensitives More paiiticularlyy it fis.

an `object tofprovidera switch Orthis4 .typepwhichx includesa pair of, sp aced`Y ,diapliragms` y.which sup.n portv the` Acontacts and which :haver substantially. the same mass, the sainecoefcientI oi'expansioni the same' vibration.;characteristics; etc.-, so that they dwill. move together in.; the ysame .direction when the temperature changes or when the switch is vibrated.

Another/object is, to provideta differential -.pres i sure' switch whichican be adjusted ywhile it is un der pressure.` Withgthe switches infusel at 'the presentftime it'is necessary to remove the'pres sure .and f disconnect .the vlterminals.- before the switch can be adjusted.

Another object is to provde'a differential'presf sure switch. which cank bewused .with `combustib-le gasy in one setfoff'chambers without riskingan explosion. L

Another object is to provide a :differential.pres-` sureswitch. which .isrmore' sensitivethan the single diaphragmi type', differential: pressure switch.;

Another Objectis to provide a Adifferentialpressure switch in which fthedi'aphragms .themselves actr as electrical conductors;

Further yobjects and'advantages of the present f invention will be apparentifrom'the following description, reference, being- .had tothe accompany" ing drawings whereinapreferred embodimentof the'present: invention is shown, lin which: t

l is affront elevational viewfoffa switch.. constructed'inaccordance withtheteachings 'of the present invention;

Fig. 2 is a. bottom Lplan .view of. thel switch;

Fig.13 is. anenlarged vertical: sectionalrview `of the, switch takenfon the. line` 3 5-3 in. Fig. 4l.;

Fig. 4 is1a vertical sectional view taken 'on the line .ll-'Jl inFg. 3;

Fig..5 is an enlarged fragmentary vertical sec-V tional view taken on the line 5"-5 in' Fig. 4;

Fig.6 isa front elevational view vof the' center ring assembly with the cover plate'removed from the uppery projection;

Fig. 7 isa radial transverse sectional view taken` on the line 1-1 of'Fig. 6;.

Fig. 8 is afragmentary vertical sectional View takenv onthev line 8-.8 in Fig'. 6;'

Fig. 9 .is..an .enlarged.fragmentary horizontalv sectional view taken .onthe line 9-,9 in Fig;

Fig..10. is a top plan view `of.' the. center. ring assembly shown in Fig. 6;

Fig.A 1l is yan .enlarged-fragmentary transverse sectional view-taken yon the line -l l-I l in Fig. .4;

Fig.. 12 gis. a fragmentaryisectional viewtaken on the line lZ--IZ in :Fig-n4; and" Fig. 13 is an v,enlarged fragmentary `vertical seca tional View taken on thezline .i3-.I3 inlFigz/l.

Referring tothe drawings more particularly by reference numerals, indicates generally a differential pressure switch embodying the teachings of the present invention.

rlhe switch 2S includes a housing having a dish-like base member 22, a center ring assembly 2d, and a cup-like cover member 26, in juxtaposition as shown in Fig. 3; the three members being fastened together by machine screws 29.

Disposed between the base member 22 and the center ring assembly 24 in a diaphragm 3|), and disposed between the center ring assembly 23 and the cover member 23 is another diaphragm 32, the two diaphragme and the three members defining an inner chamber 33 and a pair of outer chambers 34.

The diaphragms and 32 are made in the shape shown in Figs. l and 5 of preferably a resilient electricity conducting material, preferably beryllium copper, and are of substantially the same thickness and size and have substantially the same mass, the same coefficient of expansion, and the same vibration characteristics. Preferably, both diaphragms should face the same way, as shown in Figs. 3 and 5. Each diaphragm has a cylindrical contact 35 with a rounded inner end fastened adjacent the center thereof, the contacts 35 being in alignment and extending into the inner chamber for a purpose to appear.

Flat annular gaskets 36 0f rubber or like ma terial are disposed between the diaphragms and the members adjacent thereto at their marginal portions so as to seal the chambers against the escape of air or gas.

The base member 22 (Fig. 3) is perfectly circular in shape and includes a peripheral ange portion 3l which contains a plurality of spaced openings 3S formed therein to receive the free ends of the fastening screws 29.

Mounting lugs 33 (Figs. 1 and 2) extend from the periphery of the base member 22 for fastening the switch 20 to a xed support.

The cover member 26 (Figs. 1, 2 and 3) is also preferably cylindrical in shape and includes a base portion de and a peripheral flange portion The flange portion 112 contains a plurality of spaced openings 5:3 which are in alignment with the openings 38 in the base member, and which receive the head ends of the screws 29. Openings are also contained in the diaphragms and 32 in alignment with the openings 38 and d3, so that the screws 23 can pass through. The openings in the diaphragms are made larger than the others, however, so the screws 29 wont short the diaphragms.

Extending normal to the base portion 40 is a cylindrical wall 33 which forms a chamber to receive switches, relays, wiring, etc., which form no part or the present invention.

A flat cover 43 and an annular gasket 53 are removably fastened to the outer edge of the wall 3 by screws 52 (Fig. 3).

An opening 5Fl (Fig. 1) is contained in the cover and an externally threaded cylindrical electrical disconnect receptacle is fastened to the cover fill in alignment with the openings 54 by means of screws 58.

The center ring assembly 24 (Figs. 6 and l0) includes a flat annular body portion S0 and a pair of diametrically opposed upper and lower projections 'E2 and 54, respectively, which are formed integral with the body portion and extend outwardly therefrom.

The body portion 60 contains spaced openings 55 in alignment with openings 38 and 43 to receive the machine screws 29.

The lower projection 54 contains two inwardly extending passageways G5 and 63 (Fig. 4), the outer portions of the passageways containing internal threads to receive the ends of tubes or pipes which are in communication with the pressure sources, as will appear.

The passageway G0 extends through the annular body portion 60 so as to be in communication with the inner pressure chamber 33.

The passageway GS extends partially through the body portion 30 and intersects another passageway 'l0 which extends transversely through the body portion 30 (Fig. 8). Openings are contained in the diaphragms 3G and 32 and the gaskets 35 in alignment with the ends of the passageway l0. As shown in Fig. 13, angular passageways '12 and 1d are contained in the flange portions 42 and 37, respectively, and connect the ends of the transverse passageway 'I0 with the outer chambers 34. Thus, the pipe or tube connected to the outer end of the passageway 60 is in communication with both outer chambers 34, and they are in communication with each other.

As shown in Figs. 7 and 1l, a passageway '1G extends transversely through the annular body portion G5 and is in alignment with the inner end of a passageway 'Z3 which extends from the chamber 46 through a flange portion t2 of the cover member 2t. Openings are contained in the diaphragm 32 and the gaskets 3E in alignment with these passageways.

An insulated wire extends through the passageways IB-'I6 and is connected to the diaphragm 30 adjacent its edge.

Another passageway 82 (Fig. 12) extends from the chamber 45 through the flange portion e2 of the cover member 28, adjacent the passageway i8. The gasket 35 adjacent one side of the diaphragm 32 contains an opening in alignment with the end of the passageway 82.

A second insulated wire S4 extends through the passageway 82 and is connected to the diaphragm 32.

Thus, there is one electrical circuit from the wire 8), through the diaphragm 33 to the contact 35 adjacent the center thereof, and a second circuit from the wire SG through the diaphragm 32 to the contact 35 adjacent its center.

As shown in Figs. 4 and 5, the upper projection 52 which extends from the body portion E0 has a flat upper surface 36, and contains three parallel openings 88, and 92 which are of circular cross section and which extend inwardly from the surface 88 to the inner chamber 33. The outer portion of the opening S0 is slightly enlarged so as to provide a shoulder 35 inwardly of the upper surface 86.

Rigidly fastened in the openings 88 and 92 are a pair of cylindrical elongated stop members 96 which extend into the inner chamber 33 and which contain vertically extending slots 98.

Disposed in the center opening 90 is an adjustable supporting assembly which includes a screw member |00 comprising a head portion |02 which contains a slot |04, a iiange portion |06 (disposed above the shoulder 94) and a threaded body portion |08.

An annular metal washer ||0 is disposed in the opening 93 around the head portion |02 and another annular metal washer ||2 and a rubber gasket 3 are disposed between the ilange Dortion |06 ,and the shoulder 94.

Threadedly. fmounted-.;on1zthe :innemend of; there bodyiportion .1I 98. so;asgtoextendv wellintogrthei in ner chamber 3 3.-,Vv lisan ;e1ongatedfsupportingmeme` ber .I I4 fof circular, crossasectionrg.,

A resilientI strip i, I I iisg-fastened Lto ,thel inneraf." end of .the supporting .member I I4 by. meansof: f, an: insulator member I I8, in themanner.. shown; inFigiB.; Thev'strip V| I5 has a wedgeshapedmemf: ber I I8. fastened; to itszend which isfmade: of :elect i tricity conducting :material :and isdisposedazbe. tween. the kcontacts 3B/'so vthat whenfthey lare" forcedlagainst it by theA diierence.irri/pressurev between the vinner chamber 533': andi. the. outer, i ohambe1s"34,1as,will appear, an .electrical circuit is completed :between the Vltwo'f diaphragme 4andv the wires fastened thereto.'-V

Formed-y in thev supportingjmember--wl Il is la transversely extending opening lI ZIV-(Fig. l5) ,Tand disposed in theopening is a bowed, wire-like; tensA sioning i member |22' (Figi 4)-1 which-#extendsfthrough the slots 98in the stopimembers'iltl.` Thea; tensioning member=|22 contains `inwardly ycurvL ing ends' |25 which-'bear againstrtheinner face--r ofthe body.A portion 1.601,1:

As shown inFigs. f3; 4 and A6,theannular` body' portiono of lthe .center fringaassembly .2411con* tainsa groove I2i1`ofrectangular..crossesectiorny formed in itsinner face.

Bearing .strips I2I5..are :disposedin athe grooveA |26 adjacentzthe urvedends. |2501? the tension-sf ing member: I24rso rasrtc .betinislidingi-:contact withy them.:

Thus,. when the; screwtmember I 09x isil rotated by means of -`a, screw: driver :inserted inrgthe fslotij t I 04;5 the. supporting :member I I4?, :isJnovedr` lout-f.: f wardly orinwardly, a predetermined distancerdez".` pending .upon L the :,directiontiof frotation.; and t-the s wedge-.shaped member I I8 is-:moved :relative tozzf thecontacts 35" so'astopositionga portion :thereof--` of different thickness betweernthem:T Because-ther; supporting member is insulated from. theravedge-e shaped vmember I I8V byv the insulator-member fI II',` ther y:operator adjusting Athe :switchn-will.;notare@ f ceive-a shock even-if the/contacts :35eme touche ing. the wedge :shaped memberi ,I |14. i

rEhe supporting` member: II 4 is-'.prevented-fromi.f, tu rning when @the screw I 20 Yis. actuated because` the ends'of the-tensioning memberfare disposed: in the groove |26 and also beca11se the members.:

22 is .conned-.within' the :slots 93.infthe stop.;- members 95.

The :tensioning member y-I 22-v exerts a 1force..:,on the .supporting member: IIA' itendinglto move it". inwardly, and this movement is rresisted- .by thea flange portion i I iixof therscrew membenIII bearing againsttthe--washer -II21 and: gasket` 1 I3 .on theshouider 84x Thus,I the-adjustable.supportinga4 assembly is always under tension so fthatiftheref" is no; play between-theparts;f

The .outward .movement .off the. wedgeeshaped .imember -I I3 is limitedI .bythe outer end ofi thee.-` supporting member.y yI I liabutting theinnerJ-face of the., gasket I I3,-, andathee inward movement is, limited i by` the tensioning. member.r |22 i abutting L the lower ends ofthe. slots 98; in thestop members 95 Consequent1y,-. there isnochance vof the.; wedge-shaped. member. I I8 being` driven inwardlyf beyond .the contacts35w.

As. shown in Fig- 5,.. an annular .metal washer |3E isdisposed on top,of the uppenprojection, 62 of .the bodyportionf., Disposedonf.topof-,. the. washer I 39. 4is a flat, ring-like ,.membenf I 3.2, which. contains an Vopening atiitscenter vtoreceive thehead .portion I 32 of the .screw member .I 00,.

they. face in the samendireetion;

alii; e

isi a .gasket-.1I 36. and-a v.cover plate tI 38--which .are i' washers; I 40.; Thus,.whenfit is. ,desirable to adjust. I

and gasketfl 36;.carr be easily. and quickly; removed, or merely swung to oneside andoutof. theway,fr bygunloosening 1.one i screw ,-.zI 40-and .removing `the other` so as fto exposer the` head portion. I 02 inthe opening: contai-nedrinfthe ring-like `member |327.;

Theprimary seal-is `Vachieved `by means ...ofvthe 1 gasket,13,6V andthe cover plate. .I 38; butthegasket..

I I 3 alsoraidsin preventing `theescape of,r airor. ease from;the:innert. chamber-33 through .the l opening. s uf:

Wh'enfthe pressurev withinl the-.iinner.Chambon 33: fis fonlynatmospheric fpressure,-.the gasket-I I3 can be omitted and a thicker metalfwasherd L2. f

usedinplaoeoffthe Washer,andgasketrv However,

whenfthe pressurewithin the inner chamber` 3 3` is.;` greatertthan:atmospheric it. is` advantageous .to use the gasket II3 to aid in sealing the opening 1 Operation The4 switch .2 IIA has proven very successful in air:

craft Vto control' the circuit which lowers.l and raises theiaps;r In suchan installationyone end "ofiia tube IIIZis"connectedtothe passagewayj and the other end, thereof 'is connected to a static pressurearea within-the aircraft. Also, one end of a tube |44 is connected to thev passageway 68 andthe other end's connected to. aPitot tube or 4the like'outsidethe aircraft; Thus, the pressure; in the inner Ychamber 3311s substantiallythe same as the pressure withinithe static area of the air'- craft; and the pressure in the outer chambers 34'. is substantiallythe same as .the ram air pressure,v

Athe diierence betweenthe two indicating the air speed of the aircraft.v

the pressure in the outer.. `chairibers 3d" in; creasesabove the pressure intheinn-er chamber, the diaphragme 3B and {ifi-lei; slightly. ,toward 4 eachother, and when the diilerence between the two pressures reaches" the amount for which the switch' has been set, the ,contacte touchtie. wedgershaped ymember I ISI. This wiillcomplete.. the circuit through the diaphragrns ivandll y,andthewiresIIand 84so toenergisejthe relayorthelike (not shown.,V contained the chamber ,46;`

If the contacts 35 are not. touching the` wedge.Y

shaped member `I I8 and there, is .a vsudden unidie rectional impact.against.ther aircraft, both phragms williiex in thesame ydirection..so.that. even if `one diaphragm moves acertain distancetowards the Uwedge-shaped member and touches it, f the otheridiaphragm wiil vmove away yfrom the wedge-shaped, Vmember i3 a like dis tanoe'so that the distance between the inner endsl of `thediaphragms are'substantially the sa ruso, pactf is -foscillatolynboth :diaphragme: will :vibi

iny the-same manner'beeause .they l vibrationf characteristics and :I the liv-the samen; TheA the. :wedge-shapedmember I I ti when the mot-eef ment occurs. andthe member iIIwill .all ymove together with theilatter1.held..,between thetcontacts @35..f Fury-r.y

In-ethetlatter casey-the-reon-"facts 35 thermore, the same thing is true when a change in temperature occurs. Inasmuch as both diaphragms are the same size, have the same coefcient of expansion, face the same direction, and are subjected to the same temperatures, any change in temperature in the outer chambers 34 due, for example, to a change in altitude in the aircraft, will aiTect them equally and cause like movement of the diaphragms.

Because there are two diaphragms in the switch and because they .both move inwardly the same distance, each has to move only half the distance required oi a single diaphragm type switch, so that the switch 20 is twice as sensitive as the switches employing a single diaphragm.

Another advantage of this switch is that there is no arcing of any kind in the outer chambers so that it can be used in installations where it is desirable or necessary to use combustible gases in the outer chambers.

Thus, it is apparent that there has been provided a novel differential pressure switch which fuliills all of the objects and advantages sought therefor.

It is to be understood that the foregoing clescription and the accompanying drawings have been given only by way of illustration and example, and that changes and alterations in the present disclosure, which will be readily apparent to one skilled in the art, are contemplated as within the scope of the present invention, which is limited only by the claims which follow.

What is claimed is:

1. A pressure switch, comprising a housing; a pair of spaced diaphragms within the housing dividing it into an inner chamber and two outer chambers, the two outer chambers being in communication; a contact fastened to each diaphragm adjacent its center and extending inwardly into the inner chamber; adjustable means in the inner chamber for electrically connecting together said contacts at predetermined positions of the diaphragme; passage means into the inner chamber; and passage means into the outer chambers.

2. A pressure switch, comprising a housing; a pair of spaced diaphragms within the housing dividing it into an inner chamber and two outer chambers, the two cuter chambers being in communication; a contact fastened to each diaphragm adjacent its center and extending inwardly into the inner chamber; adjustable contact means of varying thickness movable between said contacts so as to provide a bridging contact between the contacts on the diaphragme when the latter are in predetermined flexed positions; passage means into the inner chamber; and passage means into the outer chambers.

3. A pressure switch, comprising a housing; a pair of parallel spaced diaphragms within the housing dividing it into an inner chamber and a pair of outer chambers, the outer chambers .being in communication; a contact fastened to each diaphragm adjacent its center and extending inwardly into the inner chamber; an adjustable supporting member in the inner chamber which contains a wedge-shaped element of electricity conducting material adjacent its inner end, the wedge-shaped element being movable between and relative to the contacts on the diaphragms so as to provide a bridging contact between them; passage means into the inner chamber; and passage means into the outer chambers.

4. A pressure switch, comprising a housing; a pair of parallel spaced diaphragms of electricity conducting material within the housing dividing it into an inner chamber and a pair of outer chambers, the outer chambers being in communication; a conductor connected to each of the diaphragms; a contact fastened to each diaphragm adjacent its center and extending inwardly into the inner chamber; and an elongated adjustable supporting member extending into the inner chamber and having a wedge-shaped element of electricity conducting material adjacent the inner end thereof, the wedge-shaped element being movable between and relative to the contacts on the diaphragme so as to provide a bridging contact between them and complete the circuit between the conductors when the diaphragms are in predetermined iiexed positions.

5. A pressure switch, comprising housing; a pair of spaced diaphragms Within the housing dividing it into an inner chamber and a pair of outer chambers; a contact fastened to each diaphragm and extending inwardly into the inner chamber; an adjustable elongated supporting member extending into the inner chamber and having a wedge-shaped element of electricity conducting material adjacent the inner end thereof but insulated therefrom; and means for adjusting the length oi the supporting member from outside the housing so as to vary the positions of the wedge-shaped element relative to the contacts cn the diaphragms.

6. A pressure switch, comprising a housing; a pair of spaced diaphragme within the housing dividing it into an inner chamber and a pair of outer chambers; a contact fastened to each diaphragm and extending inwardly into the inner chamber; an adjustable elongated supporting member extending into the inner chamber and having a wedge-shaped element of electricity conducting material adjacent the inner end thereof; and yieldable means urging the supporting member inwardly.

'7. A pressure switch, comprising a housing; a pair of spaced diaphragms within the housing dividing it into an inner chamber and a pair of outer chambers; a contact fastened to each diaphragm and extending inwardly into the inner chamber; an adjustable elongated supporting member extending into the inner chamber and having a wedge-shaped element of electricity conducting material adjacent the inner end thereof; means for adjusting the length of the supporting member from outside the housing; and means limiting the inward movement of the Wedge-shaped element.

8. A pressure switch, comprising a housing having a side wall; a pair of spaced diaphragme within the housing dividing it into an inner chamber and a pair of outer chambers; a contact fastened to each diaphragm and extending into the inner chamber; an opening the side wall; an elongated adjustable supporting member disposed in the opening and extending into the inner chamber, the supporting member having a contact bridging element of varying width adjacent its inner end; and an elongated resilient wire-like member extending transversely through the supporting member and having its ends against the inner surface of the side wall..

9. A pressure switch, comprising a housing having a side wall; a pair of spaced diaphragms within the housing dividing it into an inner chamber and a pair of outer chambers; a contact fastened to each diaphragm and extending into the inner chamber; an opening in the side Wall; an elongated adjustable supporting member disposed in the opening and extending into the inner chamber, the supporting member having a contact bridging element of varying width adjacent its inner end; an elongated stop member containing a slot therein extending inwardly from the side wall on each side of the supporting member; and an elongated resilient wire-like member extending transversely through the supporting member and the slots in the stop members and having its ends against the inner surface of the side Wall.

10. A pressure switch, comprising a housing having a side wall; a pair of spaced diaphragms within the housing dividing it into an inner chamber and a pair of outer chambers; a contact fastened to each diaphragm and extending into the inner chamber; an opening in the side Wall leading into the inner chamber; a screw-like member extending into said opening from outside the wall; an elongated supporting member having its outer end threadedly disposed on the end of the screw-like member within the opening; means preventing rotation of the elongated member in the opening; a resilient strip fastened to the inner end of the elongated member; and a wedge-shaped member of electricity conducting material fastened to the end of the resilient strip.

11. A pressure switch, comprising a housing having a side wall; a pair of spaced diaphragms within the housing dividing it into an inner chamber and a pair of outer chambers; an opening in the side wall leading into the inner chamber; a screw-like member extending into elongated member inwardly away from the screw-like member.

12. A switch, comprising a housing; a pair of opposed spaced diaphragms within the housing dividing it into an inner chamber and a pair of outer chambers; a contact carried by each diaphragm and extending into the inner chamber; a member extending into the inner chamber and supporting an element of varying thickness for movement between the contacts and relative thereto.

ELI E. HARRIS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,008,627 Place et al. July 16, 1935 2,044;729 Eggleston et al. June 16, 1936 2,454,423 Baak Nov. 23, 1948 2,479,616 Hasselhorn Aug. 23, 1949 

